The Stranger won't give anything to the player if he/she gave him a water bottle but also has an undamaged Gas Mask.

The Stranger is a reference to the player character, a vault dweller tasked to find a water chip for his/her vault from the post nuclear role playing game, Fallout. The Stranger asking for a water chip and a gas mask in return of a water bottle, is a reference to his/her mission of finding the water chip and the need of a gas mask to survive in the wasteland.